1) Field of the Invention
The invention relates to the use of water-redispersible, protective-colloid-stabilized dispersion powder compositions based on vinylaromatic-1,3-diene copolymers in self-leveling screeds and trowel-applied flooring compositions.
2) Background Art
For many years, dispersion powders have been used, particularly in the construction sector, as a polymeric improver for hydraulically setting systems. An overview of the action of dispersion powders is given in the periodical TIZ (Tonindustrie-Zeitung) 9, p. 698 (1985). Especially the properties of adhesion, wear resistance, scratch resistance and bend resistance of hydraulically setting compositions are improved by adding dispersion powders. Examples of descriptions of these dispersion powders are found in DE-A-2049114 (U.S. Pat. No. 3,784,648), and they are prepared by spray drying aqueous polymer dispersion powders with addition of polyvinyl alcohol and of other additives. The resultant powder, with good free flow and with particle sizes from 10 to 250 xcexcm, redisperses in water to give a dispersion with particle sizes from 0.1 to 5 xcexcm. This redispersion should remain stable over a prolonged period, i.e. should not show any tendency toward sedimentation.
An important application sector for dispersion powders is that of hydraulically setting trowel-applied flooring compositions. These trowel-applied flooring compositions have been disclosed in DE-A 3028559 (GB-A 2083015) and EP-A 116524, and are generally composed of cement or mixtures of different cements, carefully balanced filler combinations, dispersion powders, plasticizers and, where appropriate, other additives. DE-A 3028559 proposes modifying the compositions with comminuted elastomers and with dispersion powder based on vinyl acetate-ethylene copolymers. EP-A 116524 recommends the use of polymer powders or polymer dispersions for providing elasticity when producing flowable compositions, the polymer powders recommended being those based on vinyl ester polymers.
DE-B 2064081, DE-B 2102456 (GB-A 1325518), DE-B 2301435 and DE-B 2534564 recommend using polyvinyl acetate dispersion powders as an additive in flowable compositions. The flowable compositions are generally in dry mortar from when they are delivered to the building site, where they are simply mixed with water and spread on the floor. The materials flow out to give a smooth surface which serves directly as the wear layer or serves as substrate for further coatings. This usage always give problems. Particularly when relatively thick layers are applied, uneven areas, such as craters or pinholes, form on the surface. The surface does not become as smooth as the purchaser desires, and requires further work.
The procedure used hitherto to avoid uneven areas of this type has been to use additives. EP-A 477900 (U.S. Pat. No. 5,118,751) recommends the use of fully hydrolyzed copolymers made from 1-alkylvinyl esters and from vinyl esters to eliminate these problems. However, these additives are relatively complicated to prepare and increase the cost of the dispersion powder composition to an unacceptable degree.
It is an object of the present invention, therefore, to eliminate the disadvantages described above for known trowel-applied flooring compositions, in relation to the surface quality of coatings produced from these, without the use of fully hydrolyzed copolymers made from 1-alkylvinyl esters and from vinyl esters, but to do this without losing the advantages gained by adding dispersion powders, for example improved wear resistance, scratch resistance and adhesion.
Surprisingly, it has been found that the use of powders based on protective-colloid-stabilized vinylaromatic-1,3-diene polymers enables the use of fully hydrolyzed copolymers made from 1-alkylvinyl esters and from vinyl esters to be dispensed with, while retaining equivalent surface qualities and at the same time obtaining good wear resistance, scratch resistance and adhesion.
The invention provides the use of water-redispersible, protective-colloid-stabilized dispersion powder compositions in self-leveling screeds or trowel-applied flooring compositions, wherein the dispersion powder composition comprises
a) a base polymer selected from the group consisting of the vinylaromatic-1,3-diene polymers,
b) from 2 to 25% by weight, based on the base polymer, of one or more protective colloids,
c) from 3 to 30% by weight, based on the total weight of polymeric constituents, of fine antiblocking agent, and
d) from 0.1 to 10% by weight, based on the base polymer, of other additives.
Suitable vinylaromatic compounds are styrene and methylstyrene, copolymerization of styrene being preferred. Examples of 1,3-dienes are 1,3-butadiene and isoprene, 1,3-butadiene being preferred. The copolymers generally contain from 20 to 80% by weight, preferably from 30 to 70% by weight, of vinylaromatic compound, and from 20 to 80% by weight, preferably from 30 to 70% by weight, of 1,3-diene, and other monomers may also be present where appropriate, and the percentage by weight data always give 100% by weight in total.
Up to 30% by weight, based on the total weight of the monomer phase, of other monomers copolymerizable with vinylaromatic compounds and with 1,3-dienes may be copolymerized where appropriate, for example ethylene, vinyl chloride, (meth)acrylates of alcohols having from 1 to 15 carbon atoms, or vinyl esters of unbranched or branched carboxylic acids.
From 0.05 to 10% by weight, based on the total weight of the monomer mixture, of auxiliary monomers may also be copolymerized where appropriate. Examples of auxiliary monomers are ethylenically unsaturated mono- and dicarboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid or maleic acid; ethylenically unsaturated carboxamides and carbonitriles, preferably acrylamide or acrylonitrile;. mono- and diesters of fumaric acid or maleic acid, such as the diethyl or diisopropyl esters, and also maleic anhydride, ethylenically unsaturated sulfonic acids and salts of these, preferably vinylsulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid. Other examples are precrosslinking comonomers, such as comonomers with two or more ethylenic unsaturations, such as divinyl adipates, diallyl maleate, allyl methacrylate or triallyl cyanurate, or postcrosslinking comonomers, such as acrylamidoglycolic acid (AGA), methyl methylacrylamidoglycolate (MAGME), N-methylol-acrylamide (NMA), N-methylolmethacrylamide, allyl N-methylolcarbamate, alkyl ethers, such as isobutoxy ether, or esters of N-methylolacrylamide, of N-methylolmethacrylamide, or of allyl N-methylol-carbamate. Other suitable comonomers are epoxy-functional comonomers, such as glycidyl methacrylate and glycidyl acrylate. Other examples of comonomers are silicon-functional comonomers, such as acryloxypropyl-tri(alkoxy)- and methacryloxypropyltri(alkoxy)silanes, vinyltrialkoxysilanes and vinylmethyldialkoxysilanes, examples of alkoxy groups which may be present being ethoxy radicals and ethoxy(propylene glycol) ether radicals. Mention may also be made of monomers having hydroxyl or CO groups, for example hydroxyalkyl methacrylates and hydroxyalkyl acrylates, such as hydroxyethyl, hydroxypropyl and hydroxybutyl acrylates and the corresponding methacrylates, and also compounds such as diacetoneacrylamide and acetylacetoxyethyl acrylate and the corresponding methacrylate.
The selection of monomer here, and the selection of the portions by weight of the comonomers, is generally such as to give a glass transition temperature Tg of from xe2x88x9270 to +70xc2x0 C., preferably from xe2x88x9250 to +50xc2x0 C., particularly preferably from xe2x88x9220 to +40xc2x0 C. The glass transition temperature Tg of the polymers may be determined in a known manner by differential scanning calorimetry (DSC). The Tg can also be approximated in advance by using the Fox equation. According to T. G. Fox, Bull. Am. Physics Soc. 1, 3, page 123 (1956): 1/Tg=x1/Tg1+x2/Tg2+ . . . +xn/Tgn, where xn is the proportion by weight (% by weight/100) of the monomer n and Tgn is the glass transition temperature in degrees Kelvin of the homopolymer of the monomer n. Tg values for homopolymers are listed in Polymer Handbook 2nd Edition, J. Wiley and Sons, New York (1975).
Protective colloids suitable as component b) are for example polyvinyl alcohols, polysaccharides in water-soluble form, for example starches (amylose and amylopectin), modified starches, for example starch ethers, such as hydroxyalkyl ether starches, dextrins and cyclodextrins, celluloses and their carboxymethyl, methyl, hydroxyethyl and hydroxypropyl derivatives, poly(meth)acrylic acid, poly(meth)acrylamide, melamine-formaldehyde sulfonates, and naphthalene-formaldehyde sulfonates.
Preference is given to polyvinyl alcohols having a degree of hydrolysis of from 80 to 95 mol % and a Hxc3x6ppler viscosity of from 1 to 30 mPas in 4% strength aqueous solution (Hxc3x6ppler method at 20xc2x0 C., DIN 53015). Other suitable materials are hydrophobically modified polyvinyl alcohols having a degree of hydrolysis of from 80 to 95 mol % and a Hxc3x6ppler viscosity of from 1 to 30 mPas in 4% strength aqueous solution. Examples of these are partially hydrolyzed copolymers of vinyl acetate with hydrophobic comonomers, such as isopropenyl acetate, vinyl pivalate, vinyl ethylhexanoate, vinyl esters of saturated alpha-branched monocarboxylic acids having 5 or 9, to 11 carbon atoms, dialkyl maleates or dialkyl fumarates, such as diisopropyl maleate or diisoproypl fumarate, vinyl chloride, vinyl alkyl ethers, such as vinyl butyl ether, or olefins, such as ethene or decene. The proportion of hydrophobic units is preferably from 0.1 to 10% by weight, based on the total weight of the partially hydrolyzed polyvinyl acetate, these hydrophobically modified polyvinyl alcohols producing a surface tension  less than 40 mN/m in 2% strength aqueous solution. It is also possible to use mixtures of the polyvinyl alcohols mentioned.
Antiblocking agents suitable as component c) are known to the skilled worker. Examples of these are calcium carbonate, magnesium carbonate, talc, gypsum, silica, and silicates, such as magnesium hydrosilicate. The particle size is generally from 10 nm to 10 xcexcm.
Other components present as component d) in the dispersion powder compositions are antifoams, pigments, fillers, foam stabilizers, hydrophobicizing agents, wetting agents, and cement plasticizers. The amounts in which the constituents mentioned may be added, if desired, are those known to the skilled worker.
The protective-colloid-stabilized polymer powders are prepared in a known manner by emulsion polymerization, the polymerization temperature generally being from 40 to 100xc2x0 C., preferably from 60 to 90xc2x0 C. When gaseous comonomers, such as ethylene or vinyl chloride, are copolymerized, it is also possible to operate at superatmospheric pressure, generally at from 5 to 100 bar. The polymerization is initiated with the initiators or redox-initiator combinations which are commonly used for emulsion polymerization, for example hydroperoxides, such as tert-butyl hydroperoxide, azo compounds, such as azobisisobutyronitrile, or inorganic initiators, such as the sodium, potassium or ammonium salts of peroxodisulfuric acid. The initiators mentioned are generally used in amounts of from 0.05 to 3% by weight, based on the total weight of the monomers. The redox initiators used comprise combinations of the initiators mentioned with reducing agents, such as sodium sulfite, sodium hydroxymethanesulfinate, or ascorbic acid. The amount of reducing agent is preferably from 0.01 to 5.0% by weight, based on the total weight of the monomers.
The polymerization mixture is stabilized using the amount mentioned of the abovementioned protective colloids b), and preferably without the use of any emulsifiers. It is preferable to use the partially hydrolyzed polyvinyl acetates and partially hydrolyzed hydrophobicized polyvinyl acetates mentioned. The amount of the protective colloids generally used during the polymerization is from 1 to 15% by weight, based on the total weight of the monomers. It is preferable here for part of the protective colloid content to be an initial charge and part to be fed once the polymerization has been initiated. The monomers may be entirely an initial charge, entirely a feed, or partly an initial charge, with the remainder fed once the polymerization has been initiated.
In the preferred embodiment, the dispersion powders used to produce the flowable compositions are those in which the vinylaromatic-1,3-diene, polymer a) has been produced by emulsion polymerization of at least one vinylaromatic compound and of at least one 1,3-diene in the presence of the protective colloid b), particularly preferably without the use of any emulsifiers.
The aqueous dispersions obtainable by the processes mentioned have a solids content of from 30 to 75% by weight, preferably from 40 to 65% by weight. To produce the water-redispersible dispersion powders, the aqueous dispersions are dried, preferably spray dried. This spray drying takes place in conventional spray drying systems, and the atomization process here may take place using single-, twin- or multiple-fluid nozzles, or using a rotating disc. The discharge temperature is generally in the range from 55 to 100xc2x0 C., preferably from 70 to 90xc2x0 C., depending on the system, the Tg of the resin, and on the desired degree of drying. To ensure redispersibility, it is generally necessary to add further protective colloids to the dispersion prior to the drying process, as an aid to spraying. The amount of spraying aid generally used is from 5 to 25% by weight, based on the polymeric constituents of the dispersion. It is preferable for the polyvinyl alcohols mentioned as component b) to be admixed, in the form of an aqueous solution, with the polymer dispersion prior to the spraying process.
During or after the spraying process, the desired amount of antiblocking agent (component c)) is added. To improve performance, other additives (component d)) may be added during or after the spraying process. Examples of other constituents which may be present in dispersion powder compositions are pigments, fillers, foam stabilizers, hydrophobicizing agents, wetting agents, and cement plasticizers.
For use in self-leveling screeds and trowel-applied flooring compositions (flowable compositions), the dispersion powder composition is admixed with the appropriate mixes. It is preferable to add from 0.5 to 10% by weight of dispersion powder, based on the dry weight of the mix. The mixes also comprise from 5 to 80% by weight of inorganic, hydraulically setting binders, such as cement, gypsum or mixtures of these. Cement is preferably used as binder. Another constituent of the mix is from 5 to 80% by weight of inorganic fillers, such as sand, powdered quartz, chalk, powdered limestone, filter ash, or a mixture of these. Additives which promote flow, such as casein or cement plasticizers, may also be added to the dry mixture to improve self-leveling properties. The % by weight data here are always based on 100% by weight of dry weight of the mix for trowel-applied flooring compositions. The ready-to-use flowable composition is finally obtained by adding water to the abovementioned dry mixture.
The ready-to-use trowel-applied flooring composition, once it has been mixed with water, can be used to produce screeds or self-leveling coatings for leveling, evening or smoothing substrates. For this, the aqueous trowel-applied flooring composition is poured out, distributed and dried, generally giving layer thicknesses of from 0.5 to 30 mm. Even when applying relatively thick layers, the procedure of the invention gives smooth surfaces with outstanding mechanical strength and hardness.